Most of my residential tile work centers on the kitchen or
bathroom, but some homeowners also like the look and feel of
tile in other parts of the house. One of the most extensive
jobs we've done lately involved tiling every floor but the
staircase in a two-story, 2,500-square-foot house, including an
ornamental rug-pattern area in the great room. This was an
interesting project for us because the homeowners —
who happened to own a chain of upscale tile stores —
were unusually well informed about the latest tile installation
products and techniques.
Preparing the Subfloor
Nothing spoils a ceramic tile floor installation like a large
stress crack running across the field. To prevent this kind of
expensive disaster, I always do a little pre-installation
detective work to make sure the floor is structurally sound.
Substrate deflection is by far the biggest contributor to tile
failure. If the span is too long for the joist dimension or the
joists are too widely spaced, problems are inevitable.
For most tile applications, sticking to the standard L/360
formula (span divided by 360 = maximum allowable deflection at
center) will keep you out of trouble. The exception is natural
stone tile, which is much more susceptible to breakage than
ceramic tile. Here it really helps to have the finish floor
specified before framing starts, because the Tile Council of
America (TCA) recommends reducing the maximum deflection by
half, to L/720.
Underlayment and plywood.
Whichever deflection standard is used, the total thickness of
the plywood subfloor and underlayment-grade plywood should
ordinarily be at least 1 1/8 inches. According to TCA,
particleboard underlayment and OSB subfloor panels are not
acceptable substrate materials under ceramic or stone
Underlayment edge and end seams must be offset from those of
the subfloor by at least 2 inches to prevent telegraphed stress
cracks. The subfloor plywood should be glue-nailed to the floor
joists and the underlayment nailed off on 8-inch centers in the
field and every 6 inches around the edges. Avoid nailing
underlayment into the floor joists, because that can telegraph
framing movement to the surface (see Figure 1). To be safe, I
use underlayment nails that won't penetrate the subfloor by
more than 1/8 inch. I also gap the panel ends and edges, using
a nickel or a quarter as a gauge, to let the panels "work" a
little without stressing the tile.
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Figure 1.An uninterrupted
expanse of floor tile is prone to stress cracking. Plastic
expansion strips installed every 20 to 24 feet divide the field
into smaller zones, minimizing cumulative movement and stress.
Thermal movement at door thresholds cracks grout. It's a good
idea to install an expansion strip there, too. A minimum 1
1/8-inch-thick plywood substrate and underlayment are required
to limit deflection between framing members. Underlayment
provides added stiffness and a disconnect between subfloor and
framing movement. Proper panel layout, edge gapping, and
nailing help ensure that the underlayment performs as